Ratings in Practice

This page describes the formulae used to update the ratings scores. For more information about how ratings work see the official information page at Ratings or the unnofficial [ Ratings FAQ ].

Chess and all other games except Gammons and Salvos


These games use the old USCF ELO system which is similar to the current one. For the first 20 games, a provisional rating is used which can vary wildly. Once established, ratings change as follows. Note that it makes no difference whether your opponent is established, provisional or unrated. Usually for two players with established ratings the winner gains as many points as the loser loses. However the gains and losses are approximately 25% smaller for players rated 2100 and over.

Note that players are given a starting rating of 1200 which means that these ratings are around 300 lower than the more widespread systems centred on 1500.

Opponent's ratingWinLoseDraw
>+730+320+16
+400+29-3+13
+300+27-5+11
+200+24-8+8
+100+20-12+4
same+16-160
-100+12-20-4
-200+8-24-8
-300+5-27-11
-400+3-29-13
>-7300-32-16


Backgammon, Salvo


These games use the FIBS (First Internet Backgammon Server) rating system. A new player is assumed to be average and given a starting rating of 1500. Once you have played 400 games, ratings change as follows. Note that a multi-point match counts one game for each point. This is called your experience.

1-point3-point5-point7-point9-point
Opponentwinlosewinlosewinlosewinlosewinlose
+1000+3.0-1.0+6.1-0.8+8.3-0.6+10.1-0.5+11.6-0.4
+500+2.6-1.4+5.1-1.9+7-2+8.7-1.9+10.2-1.8
+250+2.3-1.7+4.3-2.6+5.9-3.1+7.2-3.4+8.4-3.6
0+2.0-2.0+3.5-3.5+4.5-4.5+5.3-5.3+6.0-6.0
-250+1.7-2.3+2.6-4.3+3.1-5.9+3.4-7.2+3.6-8.4
-500+1.4-2.6+1.9-5.1+2-7+1.9-8.7+1.8-10.2
-1000+1.0-3.0+0.8-6.1+0.6-8.3+0.5-10.1+0.4-11.6

There is a FIBS rating calculator at http://home.nordnet.fr/~fhochede/ratings.shtml

Until a player's experience reaches 400 games, the rating adjustment is multiplied by a factor which starts at 5 and slowly reduces by 1/100th per game to 1. Note that the further away from average a player's skill is, the longer it will take him to reach his true rating.



Tournament Ratings


These use the same formulae as above but only take into account site tournament and ladder games. They are not visible until they reach the established phase (unless you have yet to complete 20 non-tournament games and have played more tournament games than non-tournament games) when they replace the existing rating.
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This page was last edited by Mike UK at 9:01PM on 20 December 2006

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